Collisions of Cortical Microtubules with Membrane Associated Myosin VIII Tail

The distribution of myosin VIII ATM1 tail in association with the plasma membrane is often observed in coordination with that of cortical microtubules (MTs). The prevailing hypothesis is that coordination between the organization of cortical MTs and proteins in the membrane results from the inhibition of free lateral diffusion of the proteins by barriers formed by MTs. Since the positioning of myosin VIII tail in the membrane is relatively stable, we ask: can it affect the organization of MTs? Myosin VIII ATM1 tail co-localized with remorin 6.6, the position of which in the plasma membrane is also relatively stable. Overexpression of myosin VIII ATM1 tail led to a larger fraction of MTs with a lower rate of orientation dispersion. In addition, collisions between MTs and cortical structures labeled by ATM1 tail or remorin 6.6 were observed. Collisions between EB1 labeled MTs and ATM1 tail clusters led to four possible outcomes: 1—Passage of MTs through the cluster; 2—Decreased elongation rate; 3—Disengagement from the membrane followed by a change in direction; and 4—retraction. EB1 tracks became straighter in the presence of ATM1 tail. Taken together, collisions of MTs with ATM1 tail labeled structures can contribute to their coordinated organization.

Morphogenesis of stockpiled Marandu, Piatã, Xaraés and Paiaguás brachiariagrass cultivars

ABSTRACT The objective this study was to identify differences in the morphogenic patterns of four Urochloa brizantha cultivars (marandu, piatã, xaraés and paiaguás grasses) during the stockpiling period. A completely randomized design was used, with three replications, in experimental plots of 9m². The evaluations took place over 2 years. The grasses were stockpiled for 92 (Year 1) and 95 (Year 2) days. The leaf appearance rate of paiaguás grass was higher, compared to other grasses. In Year 1, the stem elongation rate of xaraés grass was higher than other grasses. At the end of stockpiling period of Year 1, the tiller population density (TPD) was higher in the paiaguás grass, intermediate in the xaraés and marandu grasses and lower in the piatã grass. At the end of the stockpiling period in Year 2, TPD was higher in the paiaguás grass canopy, intermediate in the marandu and piatã grasses canopies, and lower in the xaraés grass canopy. Paiaguás grass has greater leaf growth during the stockpiling period and is therefore suitable for use under stockpiled grazing. Xaraés grass has high stem elongation during the stockpiling period, which is why its use under stockpiled grazing must be accompanied by adjustments in pasture management.

Antagonistic cotranscriptional regulation through ARGONAUTE1 and the THO/TREX complex orchestrates FLC transcriptional output

Quantitative transcriptional control is essential for physiological and developmental processes in many organisms. Transcriptional output is influenced by cotranscriptional processes interconnected to chromatin regulation, but how the functions of different cotranscriptional regulators are integrated is poorly understood. The Arabidopsis floral repressor locus FLOWERING LOCUS C (FLC) is cotranscriptionally repressed by alternative processing of the antisense transcript COOLAIR. Proximal 3′-end processing of COOLAIR resolves a cotranscriptionally formed R-loop, and this process physically links to a histone-modifying complex FLD/SDG26/LD. This induces a chromatin environment locally that determines low transcription initiation and a slow elongation rate to both sense and antisense strands. Here, we show that ARGONAUTE1 (AGO1) genetically functions in this cotranscriptional repression mechanism. AGO1 associates with COOLAIR and influences COOLAIR splicing dynamics to promote proximal COOLAIR, R-loop resolution, and chromatin silencing. Proteomic analyses revealed physical associations between AGO1, subunits of RNA Polymerase II (Pol II), the splicing-related proteins—the spliceosome NineTeen Complex (NTC) and related proteins (NTR)—and the THO/TREX complex. We connect these activities by demonstrating that the THO/TREX complex activates FLC expression acting antagonistically to AGO1 in COOLAIR processing. Together these data reveal that antagonistic cotranscriptional regulation through AGO1 or THO/TREX influences COOLAIR processing to deliver a local chromatin environment that determines FLC transcriptional output. The involvement of these conserved cotranscriptional regulators suggests similar mechanisms may underpin quantitative transcriptional regulation generally.

Effect of Microstructure on Micro-Mechanical Properties of Composite Solid Propellant

This study was aimed at determining the effect of microstructure on the macro-mechanical behavior of a composite solid propellant. The microstructure model of a composite solid propellant was generated using molecular dynamics algorithm. The correlation of how microstructural mechanical properties and the effect of initial interface defects in propellant act on the macro-mechanics were studied. Results of this study showed that the mechanical properties of propellant rely heavily on its mesoscopic structure. The grain filling volume fraction mainly influences the propellant initial modulus, the higher the volume fraction, the higher initial modulus. Additionally, it was found that the ratio of particles influences the tensile strength and breaking elongation rate of the propellant. The big particles could also improve the initial modulus of a propellant, but decrease its tensile strength and breaking elongation rate. Furthermore, the initial defects lowered the uniaxial tensile modulus, tensile strength, and the relaxation modulus of propellant, but did not affect the relaxation behavior of the propellant.

Is organic fertilizer application a viable alternative to synthetic fertilizer for Piatã grass?

Organic fertilizer in many cases can replace mineral fertilizers and in consequence reduce production costs and improve soil quality. Thus, the aim of this work was to evaluate productive, morphogenic and structural characteristics of Piatã grass (Urochloa brizantha) fertilized with urea, organic compost and biofertilizer throughout a year. The trial design was a block split-plot in time (seasons) design with 4 treatments (fertilizing with urea, organic compost, biofertilizer and Control) and 6 repetitions. The evaluated parameters were: dry matter production (DMP), leaf elongation rate (LER), leaf appearance rate (LAR), phyllochron (PHYL), leaf lifespan (LLS), pseudostem elongation rate (SER), final leaf length (FLL), number of live leaves (NLL) and number of tillers (NT). The highest LAR values were observed during summer and spring for the treatment with urea, which also produced the highest LER values. No difference was found in SER among the fertilizer treatments but all fertilized treatments were superior to Control. NT and DMP values were highest (P<0.05) in the treatment with urea, followed by biofertilizer, organic compost and Control. In conclusion, while the use of urea provided greatest forage production, applying biofertilizer gave superior yields to organic compost. Other benefits of organic fertilizers should be assessed as well as combinations of organic and inorganic fertilizers.

Effects of stubble height and season of the year on morphogenetic, structural and quantitative traits of Tanzania grass

The objective of this study was to evaluate regrowth period (RP), morphogenetic, structural and productive characteristics of the guinea grass cultivar Tanzania [Megathyrsus maximus (syn. Panicum maximum)] under different stubble heights (SH) during dry (DS) and rainy (RS) seasons in the eastern Amazon region. The treatments were: 5, 15, 25, 35, 45 and 55 cm SH, distributed in a randomized complete block design with 6 replicates. In the 2 seasons, RP decreased linearly with increase in SH, and was considerably shorter in the RS (47 d). Leaf appearance rate decreased linearly from 0.071 to 0.051 leaves/tiller/d with increasing SH, and it was higher during the RS. Increase in SH increased leaf elongation rate, stem elongation rate and leaf area index. In the RS, climatic conditions favored the morphogenesis, resulting in higher herbage accumulation (8,693 kg DM/ha) than in the DS (2,597 kg DM/ha). In associating seasons with SH, we recommend that Tanzania grass be managed at SH between 35 and 45 cm in the DS, resulting in RP from 61 to 64 days, and at SH of 35 cm in the RS, resulting in RP of 41 days. Studies to test this management strategy seem warranted.

Trade-offs among transcription elongation rate, number, and duration of ubiquitous pauses on highly transcribed bacterial genes

In this paper, we study the limitations imposed on the transcription process by the presence of short ubiquitous pauses and crowding. These effects are especially pronounced in highly transcribed genes such as ribosomal genes (rrn) in fast growing bacteria. Our model indicates that the quantity and duration of pauses reported for protein-coding genes is incompatible with the average elongation rate observed in rrn genes. When maximal elongation rate is high, pause-induced traffic jams occur, increasing promoter occlusion, thereby lowering the initiation rate. This lowers average transcription rate and increases average transcription time. Increasing maximal elongation rate in the model is insufficient to match the experimentally observed average elongation rate in rrn genes. This suggests that there may be rrn-specific modifications to RNAP, which then experience fewer pauses, or pauses of shorter duration than those in protein-coding genes. We identify model parameter triples (maximal elongation rate, mean pause duration time, number of pauses) which are compatible with experimentally observed elongation rates. Average transcription time and average transcription rate are the model outputs investigated as proxies for cell fitness. These fitness functions are optimized for different parameter choices, opening up a possibility of differential control of these aspects of the elongation process, with potential evolutionary consequences. As an example, a gene’s average transcription time may be crucial to fitness when the surrounding medium is prone to abrupt changes. This paper demonstrates that a functional relationship among the model parameters can be estimated using a standard statistical analysis, and this functional relationship describes the various trade-offs that must be made in order for the gene to control the elongation process and achieve a desired average transcription time. It also demonstrates the robustness of the system when a range of maximal elongation rates can be balanced with transcriptional pause data in order to maintain a desired fitness.

VEGFA’s distal enhancer regulates its alternative splicing in CML

Enhancer demethylation in leukemia has been shown to lead to overexpression of genes which promote cancer characteristics. The vascular endothelial growth factor A (VEGFA) enhancer, located 157 Kb downstream of its promoter, is demethylated in chronic myeloid leukemia (CML). VEGFA has several alternative splicing isoforms with different roles in cancer progression. Since transcription and splicing are coupled, we wondered whether VEGFA enhancer activity can also regulate the gene’s alternative splicing to contribute to the pathology of CML. Our results show that mutating the VEGFA +157 enhancer promotes exclusion of exons 6a and 7 and activating the enhancer by tethering a chromatin activator has the opposite effect. In line with these results, CML patients present with high expression of +157 eRNA and inclusion of VEGFA exons 6a and 7. In addition, our results show that the positive regulator of RNAPII transcription elongation, CCNT2, binds VEGFA’s promoter and enhancer, and its silencing promotes exclusion of exons 6a and 7 as it slows down RNAPII elongation rate. Thus our results suggest that VEGFA’s +157 enhancer regulates its alternative splicing by increasing RNAPII elongation rate via CCNT2. Our work demonstrates for the first time a connection between an endogenous enhancer and alternative splicing regulation of its target gene.